Nowadays, speakers and/or microphones often comprise compound membranes which are basically a combination of layers of different materials or just a mixture of different materials.
JP 04-042699 discloses a diaphragm for a speaker made of a composite material being a composition of a thermoplastic synthetic resin fiber having a high glass transition temperature with a thermoplastic synthetic resin fiber having a low glass transition temperature being raw materials of two kinds of thermoplastic synthetic resin fibers having different glass transition temperatures heated at the forming. That is, the glass transition temperature of the composite takes a value between the individual glass temperatures and a large internal loss shall be obtained with a wider temperature range in comparison with the case with complete mixture of the two kinds of synthetic resins.
However, conventional acoustic devices suffer from a non-sufficient lifetime.